In U.S. Pat. Nos. 3,485,521 and 4,278,281 there are disclosed seals of the padlock type, in which the body is formed of a synthetic organic plastic, with a pair of apertures opening to one end of the body, and having a shackle formed of a piece of U-shaped wire having legs with reversely bent end portions. The end portions, when inserted into the body apertures, are intended to be locked therein by the fact that the end portion is maintained in a flexed condition so that the extreme end portion digs into a wall of the aperture and prevents removal. However it has been found that on occasion unauthorized persons have been able to work an end of the shackle out of its aperture without leaving evidence of tampering. It has been proposed that the ends of the shackle should be sharpened to increase their ability to dig into the aperture wall and prevent removal. However in either of the devices shown in the above mentioned patents, when excessive tension is applied to a leg of the shackle in an effort to pull it out of the housing, the end of the shackle will often pierce through the wall of the housing and protrude therefrom. Although this gives visual evidence of tampering, it has been found that the protruding end of the wire can be hazardous to personnel handling the assembled seals or the sealed article, and the provision of a sharpened end would considerably increase this hazard.